Process for treating slimes



June 4, 1940. .1. o. BETTERTON Er A1. 2,202,893 vPROCESS 0F TREATINGSLIMES Filed April 29, 1939 2 Shee'LS-Sheel 1 June 4, 1940.

J. O. BETTERTON -ET AL PROCESS OF TREATING SLIMES Filed April 29, 1939 2Sheets-Sheet 2 mman/v6 fam/iff 554i. 70 Se, .S11 jfl-'Caviar F/L TER IPatented June '4, 1940 UNITED STATES PATENT oFElcE PROCESS FOR TREATINGSLIMES Jesse 0. Betterton and Yurii E. Lebedeff Metuchen, and Donald P.Wilkes, Perth Amboy, N. J., assignors to American Smelting and RefiningCompany, New York, N. Y., a corporation of New Jersey Application April29, 1939, Serial No. 270,748

14 Claims. (Cl. 'l5-99) This invention relates to the treatment ofmetals and selenium. For example, typical slimes slimes, which term, asused herein, is defined as contain considerable lead and smaller amountsthe finely-divided materials comprising selenium, of other elements suchas antimony, arsenic, precious metals and other values which result tin,tellurium, etc. and copper,

from the electrolyiic Copper refining process and Now, proceeding inaccordance with the in- 5- which are various referred to as anode muds.vention and with particular reference to Fig.

slimes, sludges, etc. 1, the slimes are first treated for the removal ofAmong other features and advantages, the copper. This may be done inseveral manners,

present invention provides an improved process as by roasting and thenleaching with sulphuric for treating slimes which permits an ellcientacid solution, or by direct leaching with copper separation of thevalues to be accomplished at refining electrolyte in accordance withUnited sufllciently low temperatures that ordinary iron States LettersyPatent No. 2,031,299 granted Febrefinery kettles may be employed in theoperation. ruary 18, 1936 to Jesse O.`Betterton and George Generallyspeaking, the invention embraces H. Weis.

removing copper from the slimes and converting The leached slimes arethen fused with caustic the selenium content of the copper-depleted sodaand coke over a lead bath to form the twoslimes to reduced soluble formover a metal bath layer charge previously mentioned. Thisoperacomprising lead under such conditions that there tion-may beconducted as follows: lead, which is produced a fluid two-layer charge,the bottom may be appropriately common, refined or antilayer of whichcontains the precious metals and monial, and caustic are melted in anordinary lead contents nf the slimes while the upper layer cast ironrefinery kettle-provided with the usual contains the selenium. The twolayers are then mechanical mixer. The slimes are mixed With separatedand processed separately for recovery coke and the resulting mixturegradually fed of their respective values. to the vortex created by themixer thereby thor- More specifically, the invention contemplates oughlyincorporating the mixture inthe bath, the 25 fusing decopperized slimesover a lead bath with operation being conducted at a temperature notcaustic alkali and coke or other suitable reducing exceeding 1250" F.and preferably between 1000D agent, with or without the addition ofsteam F. and l100 F. and preferably in the presence of sulphur in Theamounts and proportions of caustic soda,

available sulphide form, to yield the thoroughly coke and lead useddepend, of course, upon the 30 liquid two-layer slag referred t above.By reaquantity of slimes treated and, also, upon their son of thefluidity of the slag, the metallic lead analyses. Thus, sufficient leadis used to insure and precious metal fall freely therefrominto the athoroughly liquid charge and adequately serve layer of molten lead belowwhile at the same its function as a collector of the precious metals;

time the selenium and tellurium are converted to, coke is used in amountsuiicient to insure comand retained in the slag as, reduced alkalicomplete reduction of the `lead content of the slimes pounds which arereadily amenable for subseto the elemental form; and enough caustic sodaquent treatment and recovery. is used to maintain a, thoroughly moltenslag at The invention further consists in the new and the temperatureemployed and to insure the connovel 'features of operation and the newand version of the selenium and tellurium to alkali 40 originalcombinations of steps in the process compounds thereof in reduced,water-soluble hereinafter described and more particularly set form.Experience has shown that, as a general forth in the claims. rule, andbased on the weight of the slimes to be The invention may be betterunderstood by treated, from 1% to 2% coke, 35% to 45% caustic ireference to the drawings accompanying and soda, and 40% to 50% lead areadequate for the forming a part of this specification inwhich properperformance of theprocess.

Fig. l is a flow sheet of the process of the in- It has been found inmaking the kettle fusion vention Iin its preferred form, and 1 that theefficiency of the operation may be en- Fig. 2 is a flow sheet of amodified form of hanced by introducing dry steam into the molten 5o theprocess of the invention and may be conslag layer, the steam apparentlyserving to re- 50 sidered as alternative to that shown in Fig. l.generate'the caustic alkali as it has been found In connection with thepresent process it that the amount of causticl soda required when shouldbe borne in mind that the slimes contain, steam is used is about 5% lessthan that renormally, as they come from .the electrolytic quired vwhenthe steam treatment is omitted. tanks, various constituents other thanprecious It is to be mentioned with respect to the amount of causticsoda used that, while same must be sufiicient to convert all theselenium and tellurium to their respective alkali compounds, any greatexcess is to be avoided for economic reasons and to assure a low leadcontent in the slag. Hence, from the standpoint of conserving caustic,the optional steam treatment is advantageous. Common vsalt may be addedto the caustic soda. to lower the melting point of the slag. Also, thecaustic may be in part replaced by other suitable alkali compounds e. g.soda ash, so long as the quantities used are compatible with properfluidity of the slag at the temperature of operation.

When the last of' the slimes have been thoroughly incorporated in thecharge, themixing is discontinued and the charge allowed to settle for ashort period so that any metallic lead and precious metals still in thefiuid slag may pass therefrom into the bath of lead below. A separationis then effected betwen the two layers, the lower or lead layer whichcontains the precious metals being transferred to the cupel furnace.Following cupellation the dor is sent to the parting plant and a part ofthe litharge reduced to metallic lead and returned to the process fortreating additional slimes in a subsequent kettle charge.

The kettle slag which contains such of the slimes constituents asarsenic, antimony and tin in addition to the selenium and tellurium, isgranulated by adding it to water, sulphur being added during thegranulation if desired or necessary as hereinafter explained;

Granulation is immediately followed by agitation, filtering and washing.the filtrate containing substantially all of the selenium and telluriumas well as the bulk of the arsenic and tin with the press cakecontaining the precious metals, the bulk of the antimony and very littleselenium or tellurium. l

The filtrate is acidified with sulphuric acid and filtered yielding anarsenic-bearing filtrate which is free from selenium and'tellurium andis discarded. The precipitate of selenium, tellurium and tin is sent tothe selenium plant for recovery of those values.

The press cake is subjected to an oxidizing roast, leached and filtered,the filtrate being evaporated to recover the selenium and telluriumcrystals which are sent to the sellenlum plant. The residue from theleach contains the gold, silver and antimony and may be suitably chargedto a lead softener or other` smelting furnace.

An important and interesting feature of this process is the role playedby sulphide sulphur in effecting solution of the tellurium with theselenium when the kettle slag is granulated in water. Usually the slimesbeing treated contain substantial amounts of lead sulphate which isreduced to metallic lead during the fusion, the sulphate radicalreacting to yield sulphide sulphur in the melt and is available to exertits beneficial action.

The exact mechanism of this reduction is unknown and may occur along oneor more different lines. Thus, the coke may reduce the lead sulphate tolead sulphide, the latter reactingwith the alkali to yield odiumsulphide which in turn reacts upon the se enium and tellurium contentsof the slimes. Or, the sulphide sulphur may be produced as the result ofseveral reactions which may be visualized in part as the reduction ofsuch compounds as sodium sulphate, sodium plumbite and sodium plumbate,resulting from the reaction of lead sulphate with caustic, to yieldsodium sulphide.

In any event, it has been definitely established that if the originalslimes are low in lead sulphate, it is necessary to add sulphur, eitheras such or as a suitable sulphur-yielding compound such as sodiumsulphide or lead sulphate (with additional reducing agent, ifnecessary), to the kettle slag before granulation if one is to throw thebuik of the tellurium with the selenium in the filtrate followinggranulation of the kettle slag. 'I'his strongly indicates the presenceof the tellurium as more or less complex sulpho-tellurides.

In addition to rendering substantially all the tellurium soluble, thepresence of the sulphide sulphur assures complete recovery of theselenium since any selenium present in soluble selenites that escapedreduction in the original kettle treatment or which may have been formedincident to granulation of the kettle slag, is readily precipitated inthe presence of sulphide sulphur upon neutralization of the filtrateobtained following granulation of the alkali kettle slag.

The beneficial effects of the above-indicated desirable reactions ofsulphide sulphur with respect to the tellurium and selenium are readilyassured in practise simply by adding a small amount of sulphur to eachkettle slag prior to granulation as a precautionary measure.

While it is preferred to have the tellurium follow the selenium asoutlined above (adding sulphur or sulphides, e. g. sodium sulphide, ifnecessary), the kettle slag may be treated by an alternative processsuch as illustrated in Fig. 2 of the drawings, wherein the kettle slagis granulated and filtered to yield a filtrate containing the bulk ofthe selenium and a relatively small amount of tellurium and a press cakecontaining the bulk of the tellurium and a relatively small amount ofselenium.

In such case the filtrate may be treated as previously described whilethe precipitate may be roasted to volatiiize selenium oxide and theresidue treated for the recovery of tin and other values. oxidizingroast, leached and filtered, the residue smelted for the recovery ofgold, silver and antimony and the filtrate neutralized to precipitatethe tellurium leaving the selenium in solution and from which it isrecovered. y

'I'he alternative process just described for treating the kettle slag iswell adapted for use when the raw slimes are substantially deficient inlead sulphate or are subjected, after decopperizing, to a soda ash leachas indicated in Fig. 2 whereby the lead sulphate is converted tocarbonate which when reduced by coke or other suitable reducing agent inthe presence of caustic soda yields lead and soda ash, the latterbeingthus available for reaction with the selenium and tellurium oftheslime and thus effect a saving of caustic. In such cases, the fusionswill lack the requisite sulphur to maintain the tellurium in the kettleslag in solution upon granulation, so that the operator has the choiceof either adding sulphur to the kettle slag before or at the time ofgranulation, or of following the alternative procedure above outlined.

The following specific example will serve to illustrate the efficiencyof the invention in effecting ya separation between the selenium andprecious metal contents of typical slimes: a fusion was made of 12 partslead, l5 parts caustic, approximately one-half part coke and 27partsleached The press cake may be subjected to an carcassa It will beunderstood thatfthe term sulphur.=

vslimes assaying 17.5% water, 3.46% selenium, 1.48% tellurium, 9.28%lead, 155.2 oz./T gold, 12,632 oz./T silver, 5.92% antimony, 2.26%arsenic, 0.65% tin and other minor impurities. f

The operation was conducted in an ordinary cast. iron kettle at atemperature of approximately 1100 F., the coke being added to the otherkettle ingredients in three portions over a mixing period of about onehour.v D rysteam was introduced with each coke addition and the slagremained fully liquid throughout the operation.

A separation was then eected between the two layers and each assayed.The slag layer showed 4.7% selenium, 1.18% tellurium, 0.5% lead,0.35oz./T gold and 128.6 oz./T silver. The

metal layer, which was 25.5 parts 'by weight,`

showed only a trace of selenium, a bit more tellurium, 158 oz./'I' goldand 12,747.9 oz. /T silver. The respective layers were then separatelytreated for recovery of their respective values as hereinbeforeoutlined.

The alternative process (Fig. 2) is illustrated by the followingspecilic example: 50 parts by weight of Wet decopperized slimes'containing 13.2% water were`1eached with an aqueous ,solutioncontaining 7.5 parts by weight of l soda ash. The leaching wasaccomplishedl in three hours time during which open steam jets wereintroduced into the leaching tank to heat and agtate the solution. -Theslimes were then ltered and the ltrate, whichcontained no values, wasdis- Y V carded.

after.

The press cake from the filtration was found Ato analyze, on a drybasis, 5.45% selenium, 1.1%

tellurium, 16.2% lead, 6.7% antimony, 170.8 oz./T gold, 15,525.2 oz./Tsilver, 1.02% arsenic and 0.10% sulphur. This indicated an excellentelim. ination of sulphur along with some arsenic by the soda ash leachinasmuch as the original decopperized slimes showed 1.78% arsenic and3.67% sulphur on a dry basis.

Thirty parts by weight of the desulphurized press cake (9.7% moisture)were subsequently mixed with 0.7 part by weight of powdered coke andgradually charged to the Vortex created by a mixer in a kettlecontaining a` molten bath of 16 parts by weight of lead and 12 parts byweight of caustic. The timeconsumed iin making the addition was twohours thirty-five minutes during which the temperature of the fusion wasmaintained between 1000 F. and 1180 F. Mixing was continued for anadditional iifteen minutes after the last of the slimes had been charged`following which the bath was settled for twenty The metal, which Was34.7 parts' by weight,

assayed 136.1 ca /T gold, 12,662 oz./T silver, 0.3% tellurium and 0.1%selenium whereas the slag, 17.1 par'ts by weight, contained 8.48% totalselenium (8.19% soluble selenium), 0.98% total tellurium' (a tracesoluble), and only 0.9% lead.

In making the fusion according to the invention the operator has a Widechoice as to the particular procedure followed' in adding the coke.Thus, it may be mixed with` the slimes prior to char ing the latter, ora portion of it may be so ggd and the remainder added after the slimescharged first and all of the coke added thereducingagent inthe process,others may be employed. Thus, natural gas and crude heavy oils have beensuccessfully used.

ave been charged, or the slimes may be Also, while coke-is preferred asthe re` form but which is rendered available as sulphur by reactionstaking place in the fused slag.

It will be apparent from the foregoing descriptions that the presentinvention provides many advantages in slimes treatment. Thus, itprovides an eiiicient low temperature process which avoidsthevolatilization losses of prior art high temperature processes andpermits wide latitude in the choice of equipment for its use. Further,inasmuch as the separation of the selenium from the precious metals isbased primarily upon conversion of the former to alkali compounds inreduced water-soluble form, proper control of the process is obtainedmuch more readily in practise than is the case, for example, withprevious proposals in which the eiciency of the treatment dependsto alarge extent on obtaining the selenium in a particular oxidized state.Also,

the precious metal and lead contents of the slimes from the selenium andtellurium contents thereofis readily obtained with a minimum consumptionof alkali reagent and, in addition, practically all of the selenium andtelluri-um in the slag can be readily separated in aqueous solution fromthe other slag values by the presence of. an adequate amount of sulphidesulphur therein.

What is claimed is: :1. The process for treating slimes which comprisesremoving copper therefrom, fusing the decopperized slimes with a slagcomprising caustic soda in the presence of a reducing agent and over abath comprising lead to form a two-layer charge consisting of a liquidslag layer and a liquid metal layer, andseparately treating said layerstortille recovery of their respective values. '2. The p cess accordingto claim l characterized in that the fusion is accompanied by theaddition of dry steam.

3. The process for treating slimes which comprises leaching coppertherefrom, converting the selenium and lead contents of the slimes tohighly reduced alkali compounds and metallic lead, respectively, over alead bath whereby precious metals and the reduced lead separate from theselenium compounds and enter the lead bath, recovering precious metalsfrom said bath, placing said reduced alkali compounds .in solution,

Y and recovering selenium from the solution.

4.' The process for treating leached slimesY in an ironvessel whichconsists in establishing a molten charge comprising lead and causticsoda in said vessel, incorporating the slimes in said charge in thepresence of a carbonaceous reducing agent while maintaining theoperating temperature below 1250 F., settling the charge, separating theslag layer of the settled charge from the underlying leadlayerfrecovering Vprecious metal values from the latter layer,granulating the slag layer to obtain a liquor containing the bulk of theselenium and a residue` containing any precious metals present in thegranulated slag, and treating said liquor for the recoveryhighly reducedalkali compounds and in rsuch form separated from the precious metalco'nstituents ofthe slimes,- the improvement which comprises granulatingthe said alkali compounds in water in the presence of sulphur therebyconcentrating the selenium and tellurium in the` liquor, ltering theliquor immediately after granulation, acidifying the ltrate'toprecipitate .selenium and tellurium, and recovering selenium beingconducted over a lead bath sewing as a collector for the preciousmetals, the improvement which consists in adding suflicient coke to thecharge to reduce lead compounds to metallic lead and assure the presenceof the selenium in alkali form in its highest state of reduction.

8. In a. process for treating slimes wherein the selenium and telluriumare -converted to highly reduced alkali compounds and in such formseparated from the precious'metal constituents of the slimes', the stepsof granulating said compounds'in water, filtering, treatingA thefiltrate to recover selenium, roastingv and leaching the filter cake,recovering tellurium from the leach solution, and smelting the residuefor recovery of precious metals.

9. Intreainng leached slimes with molten causticalkali over a metal bathserving as va collector for the precious metals of the slimes, theimprovements which consist in conducting the operation at a temperaturenot greatly exceeding 1200 F. and in the presence of suilicient reducingagent to convert the selenium and tellurium to highly reduced alkali'compounds and convert lead compounds in the slimes to metallic lead.

10. The process fortreating slimes containing 40 precious metals,selenium and tellurium, which comprises removing copper therefrom,fusing the resulting decopperized slimes with a slag comprising causticalkali in the presence of a reducing agent and over a molten bathcomprising lead to form a charge consisting of a liquid slag layeroverlying a liquid metal layer, and adding sulphur to the slag therebyconcentrating the selenium and tellurium in the slag layer as solubleselenides and tellurides while simultaneously ef.-

fectlng a concentration of precious metals in the metal layer.

11. The process for treating slimes containing selenium and telluriumwhich comprises reacting the slimes in substantialy decopperizcdcondition with a molten caustic'alkali slag over a layer of molten lead,the reaction being conducted in the presence of suliicient reducingagent to maintain substantially all of the selenium and aacasestellurium as selenides and tellurides and thereby eilect a concentrationof selenium and tellurium in the slag, separating the slag from the leadlayer and treating the slag to separate and concentrate the seleniumfrom the said slag while leaving tellurium concentrated in the residualslag, and recovering the said selenium and the said tellurium.

12. In the treatment of leached slimes, the improvement which consistsin reacting the slimes at temperatures not substantially in excess of1200" F. with an alkali slag, added sulphur and suflicient carbonaceousreducing agent to maintain the oxidizable slimes constituentssubstantially entirely `in reduced condition, the said slag floating ona molten metal bath comprising lead and serving as a collector ofprecious metals from the slimes.

I3. The process for treating slimes containing precious metals,selenium, tellurium, antimony, tin and lead which comprises treating theslimes to substantially decopperize the same, leaching the resultingdecopperized slimes with a soda-ash solution thereby converting the leadcontent of the slimes to lead carbonate, separating the residueresulting from said leach and fusing it with caustic soda and reducingagent over a molten'metal bath comprising lead at an operatingtemperature below 1250 F. thereby forming a two-layer charge of whichthe caustic soda fusion forms the top layer and the metal bath thebottom layer, causing the precious metals and lead reduced from the saidlead carbonate to enter the metal layer, effecting a separation of theslag from the enriched metal layer, granulating the slag in water toobtain a solution containing substantially all of the selenium and tin,and a residue containing substantially all of the tellurium. andantimony together with any precious metals that may have been retainedby the slag, and treating the said residue, solution and metal bath forthe recovery of their respective values.

1'4. The process for treating slimes containing both selenium andtellurium `which comprises subjecting the slimes, lafterdecopperization, to an alkali leach, fusing the leach residue withalkali compounds in the presence of reducing agent over a molten bathcomprising lead to form a two-layer charge, effecting a separationbetween the two layers, and granulating the upper slag layer in thepresence of sullicient sulphide sulphur to assure the bulk of teluriumentering the solution with the selenium.

JESSE O. BETTERTON. YURI'I -E. LEBEDEFF. DONALD P. WILKES.

